The present invention relates to a solar collector of the heat pipe type which is selfprotected against internal overpressures. It can be used in installations which employ solar collectors.
Conventional solar collectors are known. They comprise a case or container containing a solar energy absorber fixed to a heat extraction system, an insulant placed between the absorber and the case in order to reduce the heat losses by conduction, one or more glass partitions for reducing the heat losses by convection and radiation and the devices necessary for the assembly and sealing thereof.
The heat pipe is also known. It is in the form of a generally elongated container, which contains a fluid vapourizable under the normal conditions of use of said heat pipe. It makes it possible to effect a heat transfer by vapourization at one of its ends, called the hot end, and by condensation at the other end, called the cold end of a heat transfer fluid in the vapour phase, which will be called hereinafter the heat pipe fluid. In general, the heat pipe is internally lined with a capillary system and is inclined in such a way that the cold end is raised with respect to the hot end. This makes it possible to ensure the return of the heat pipe fluid both by gravity and by capillarity after the condensation thereof.
When a solar absorber is joined to a heat pump, a conventional known heat pipe absorber is obtained. A description thereof is provided, for example, in French Pat. No. 7,442,799 filed on Dec. 18, 1974 and entitled "Device for energy transformation of absorbed or emitted energy", in the name of DORNIER SYSTEM GMBH.
In this type of apparatus, the heat pipe functions as a simple heat pipe of the type described hereinbefore. The heat applied at the hot end in this case comes from the plate joined to the heat pipe and which constitutes a solar energy absorber.
The inner walls of the heat pipe are lined with a capillary system making it possible for the heat pipe fluid to rise up to the heat collecting plate. This capillary system can be constructed in various ways. It can, for example, be constituted by a fine metal wick and the heat transmitted by the upper plate then vapourizes the heat pipe fluid.
The heat applied during the condensation of the heat pipe fluid is recovered by a heat extraction device positioned, in the same way as for the aforementioned heat pipe, at the high end of the heat pipe collector, which is inclined thereto by a few degrees relative to the horizontal so as to ensure the return of the heat pipe fluid by gravity. This heat extraction device, of which several types are known, uses a fluid which is called hereinafter the primary fluid and which circulates in a duct of said primary circuit.
This type of collector makes it possible to separate the absorption function from the transfer function by the heat extraction fluid.
However, an incident which frequently occurs with this type of installation is the stoppage of the removal of heat by the primary fluid, due for example to a breakdown in the pump which circulates this fluid or to a mechanical fault. This can be prejudicial both to the collector and to the primary circuit. Thus, the heat pipe continues to transmit heat to the primary fluid whilst the latter is no longer circulating and this leads to a temperature rise which can bring about the boiling of the primary fluid and can even fracture the ducts in which it is circulating. Furthermore, the pressure within the heat pipe, which is equal to the vapour tension of the heat transfer medium, increases due to the temperature rise, which damages the actual collector.